Inflammatory bowel disease (IBD) is characterized by chronic, relapsing intestinal inflammation producing debilitating symptoms of diarrhea, abdominal pain and malnutrition. Its main forms are Crohn's disease and ulcerative colitis. Crohn's disease is characterized by transmural intestinal inflammation with granuloma formation. Defects in innate immunity, autophagy, endoplasmic reticulum (ER) stress and abnormal enteric microflora all contribute to Crohn's disease. Endoplasmic reticulum stress induces autophagy and impairs killing of pathogenic bacteria. The presence of misfolded plasma membrane and secreted proteins causes ER stress. Protein disulfide isomerases repair misfolded proteins and reduce ER stress. Anterior Gradient 2 (AGR2) is a protein disulfide isomerase expressed in intestinal secretory cells and macrophages. Human AGR2 genetic variants that decrease its expression are associated with increased IBD risk. To understand the role of AGR2 in IBD we generated Agr2 germline and conditional knockout mice. These Agr2-/- mouse models develop dramatic ileitis, colitis, multinucleated giant cells and granulomas, a characteristic Crohn's disease patient feature that has not been previously observed in any mouse model of a human IBD risk gene. Intestinal goblet, Paneth cells and macrophages have increased ER stress. p62 and LC3-II, essential autophagy genes, accumulate with AGR2 knockdown. Importantly, we have cultured mucosally adherent and invasive E. coli (which we and others have found in the ileum of Crohn's patients) from Agr2-/- ileal microflora. The overall goal of this project is to understand the mechanism of Agr2-/- intestinal epithelia, macrophage and abnormal host microflora interaction to cause multinucleate giant cells, granulomas, ileitis and colitis.